Mr Assange has told left-leaning activist group GetUp! that Ms Gillard defamed WikiLeaks when she allegedly told a radio station in 2010 he had broken the law by releasing hundreds of thousands of US diplomatic cables, according to a statement released by the group.

"I have hired lawyers in Sydney and they are investigating the different ways in which we can sue Gillard over this statement," Mr Assange told GetUp!

In late 2010, Ms Gillard said of the WikiLeaks release: "I absolutely condemn the placement of this information on the WikiLeaks website. It's a grossly irresponsible thing to do and an illegal thing to do.